Muscles, Skeletal muscles and contraction

Question 1

Muscles are:

Answer 1

Specialized cells capable of generating force

Question 2

What are types of muscle?

Answer 2

Smooth
Skeletal
Cardiac

Question 3

Where in body are muscles?

Answer 3

Skeletal- limbs, breathing muscles,eye,tongue.
Smooth in walls of blood vessels,GI tract, uterus.
Cardiac in heart

Question 4

Which types of muscle have stripes and why?

Answer 4

Skeletal, due to alignment of myosin and actin filaments and cardiac. Smooth muscle cells are not striated

Question 5

Size of muscles, number of nuclei, Control

Answer 5

Skeletal: large diameter and length, extending entire length of muscle, many nuclei, controlled by somatic NS.
Cardiac fibers are small,one or two nuclei, have specialized junctions allowing to contract as one unit, modulated by autonomic NS.
Smooth. Often spindl shaped, as sheet of cells, tighr junctions, controlled by autonomic NS

Question 6

Common principles of muscle

Answer 6

sliding filament mechanism: Myosin filament binds and move actin filaments to shorten muscle cell(contraction), regulated by calcium ions, changes in membrane potential lead to contraction its excitation-contraction coupling

Question 7

How is build muscle cell?

Answer 7

Many myofibrils composed of actin and myosin molecules, myofibryle is divided in sarcomeres.

Question 8

What is the function of Z-lines in sarcomere?

Answer 8

Borders of sarcomere, end

Question 9

What is actin?

Answer 9

Protein sticking out of z line, thin filaments, light, called I bands

Question 10

What is myosin?

Answer 10

Motor protein, towards z lines,thick filaments, dark, Called

A bands

Question 11

How is contraction formed?

Answer 11

Heads of myosin = cross bridges walking towards z lines, along the actin, sarcomere shortens, I band shortens, myosin and actin are more interdigitated. Contraction generates tension, but not necesarily shortening.

Question 12

What regulates contraction and how?

Answer 12

Calcium ions. Increase in calcium, binding to troponin causes tropomyosin to be removed from myosin binding sites on actin.in smooth muscle calcium modifies myosin.

Question 13

What is tropomyosin?

Answer 13

Tropomyosin running parallel along actin. Binding actin at site where myosin would bind, so it prevents myosin,from binding actin when there is no calcium.

Question 14

What is required for contraction?

Answer 14

Energy from ATP

Question 15

What happens when there is no ATP?

Answer 15

Rigor state, myosin head emanates from thick filament and bounded to actin causes stiffness of muscles.

Question 16

What does ATP do in contraction?

Answer 16

ATP causes myosin to let go of actin filament. ATP hydrolisis, myosin head ratchet forward and binds, release of phosphate causes power Stroke.release of ADP causes rigor state.

Question 17

When relaxation occurs?

Answer 17

When Ca+ is removed.

Question 18

Where is Ca+ stored in skeletal muscle?

Answer 18

Within cell in sarcoplasmic reticulum (SR). SR wraps around myofibrils.

Question 19

What is the cause of release Ca+ into the cytoplasm?

Answer 19

Eletrical signal which is action potential. AP opens voltage gated Ca+ channel in the T- tubule.

Question 20

What is T-Tubule?

Answer 20

T-tubule is invagination of plasma membrane, adjacent to SR. T-tubule membrane contains voltage gated Ca+ channels called dihydropyridine receptor. Activation of that receptor opens a Ca+ channel in SR (ryanodine receptor) and Ca+ enters cytoplasm. Ca+ is taken back up by into SR from cytoplasm by SR CaATPase

Question 21

E-C coupling

Answer 21

Electrical events trigger contraction. Skeletal muscles are innervated by alpha motor neurons. AP at muscular junction releases acetylcholine and it binds to nicotinic receptor on post synaptic muscle. Ligand gated Na+ channels open resulting in graded potential. Sufficiently large to depolarize sarcolemma to threshold. Voltage gated Na+ channels open and trigger AP. As AP moves along the muscle membrane it opens dihydropyrine receptors and triggers release Ca+ from SR. Contraction ensues. During contraction SR CaATPase removes Ca+ from cytoplasm and it will restore cytosolic Ca+ levels in less than 30ms after nerve impulses stops.